1. Field of the Invention
The present invention relates generally to inspection apparatus that detect the defects on an inspected object by the use of, for example, a stroboscope and, more particularly, is directed to an inspection apparatus that is equipped with a suitable stroboscope luminous energy correction function.
2. Description of the Prior Art
The stroboscope as an irradiation lamp, owing to its extremely short flash time period, has been used as the lighting device for tachometers from old times, or conventionally used to make static images of moving objects.
Further, during the recent years, the stroboscope is frequently used as the lighting device for inspection apparatus that utilize a video camera and a signal processor to detect the defects on moving objects.
FIG. 1 shows a block diagram of a conventional inspection apparatus that uses a stroboscope, a video camera, a signal processor and so on.
In FIG. 1, a belt conveyer 1 is a transfer means that conveys thereon inspected objects 2 in the direction indicated at A. With belt conveyer 1 in the middle, placed in counter facing manner are a light irradiation unit 3A and a light receiving unit 3B so that they provide a position detecting device 3 which detects the position of the inspected object 2 when the inspected object 2 arrives at a predetermined inspection position. When the inspected object 2 at the inspection position shields the light emitted from the light irradiation unit 3A, a position detection signal is generated from the light receiving unit 3B.
A power source 4B is the irradiation power source of a stroboscope 4. A flash unit 4A is placed to face downwards from an angle at above the conveyer 1, so that it irradiates the inspected object 2 which arrives at the inspection position. When the inspection position detection signal from the light receiving unit 3B is received, the stroboscope power source 4B drives the flash unit 4A of the stroboscope 4 so that the stroboscope flash unit 4A irradiates the inspected object 2 at the inspection position. The stroboscope 4 consists of the stroboscope power unit 4B and the stroboscope flash unit 4A.
A video camera 6 picks up the inspected object 2 that arrives at the inspection position and is irradiated by the stroboscope flash unit 4A. Video camera 6 is therefore placed above the belt conveyer 1 looking down so as not receive the light from the flash unit 4A directly. Signal processor 5 conducts the signal processing of the video signal from video camera 6 in order to detect the defects on the inspected object 2, when it receives the inspection position detection signal from the light receiving unit 3B.
The conventional inspection apparatus using such stroboscope as arranged above functions as following description. That is to say, even though the inspected object 2 is being conveyed on the conveyer 1, by the flashing characteristics of the stroboscope 4 that flashes within extremely short period of time, at the inspection area that receives the position detection signal from light receiving unit 3B, the video camera 6 picks up the object 2 as a practically static image.
Therefore, due to the flash characteristics of the stroboscope that flashes within an extremely short period of time, the defect detection quality deterioration of the inspected object due to its movement is eliminated, so that inspection of the inspected object is conducted with good precision.
However, at the inspection apparatus that use such conventional stroboscope, since the flash unit 4A of the stroboscope 4 normally use a Xenon tube, with long term use where its flashing numbers is great, as shown by a solid line curve C in FIG. 2, the luminous energy variation of the Xenon tube occurs, so that there was the inconvenience that the luminous energy thereof drops by the span of life of the Xenon tube.
Further, along with the improvement of the processing precision of the processor of signal processing, any variation in the luminous energy of the flash unit in the stroboscope, whether it be minor or small, there was the inconvenience that great influence is caused to the judgement precision of signal processing.